In recent years rapid innovations and developments have occurred with electronic products. With the continuous advance of semiconductor manufacturing technologies, electronic products have become more powerful and their prices have dropped. They are now widely accepted by the general public. Nowadays there are a wide variety of electronic products on the market. For the driving motor bearings used in information storage devices, there are oil impregnated bearings, ball bearings, and the like. The oil impregnated bearing has a lower price and thus cost advantage. However, its service life is shorter. The ball bearing has a longer service life, but it is more expensive and has a lower capability to withstand impact. These two types of bearings have their spindles in contact with the inner walls of the bearings. As a result, the motor tends to generate vibration and noise, and its service life becomes lower. On the other hand, dynamic bearings also are frequently used in the industry. The dynamic bearing is more precise and has a longer service life. It has become the mainstream in the market. However, it has starting friction and wearing problem that has yet to be overcome. Moreover, its production cost is higher, and production yield still does not reach the level desired. These issues remain to be resolved.
It is well known that magnets of the same polarity repel each other. This property can be used to reduce wear when the spindle rotates. This has gradually become an important research and development direction in the industry. Some techniques are known in the art. For instance, FIG. 5 discloses the conventional magnetic suspension bearing. It has magnetic portion 700 installed on the stator 800, and a spindle 500 has a permeance ring 600. However, this conventional magnetic suspension bearing has only one magnetic portion 700 and the permeance ring 600 to generates suspension, so its C.M. 900 (center of mass) is unstable and vibration and obliquity is easily occurred. FIG. 6 shows another conventional magnetic suspension bearing. It has magnetic portion 210 (made of permanent magnet) installed on the stator 200. An upper-inner permeance ring 310 (made of magnetic material), lower-inner permeance ring 320 (made of magnetic material) located respectively on the top side and the bottom side of the spindle 300. A ball bearing 400 (or a self-lubricated sleeve) is located between two ends of the spindle. However, the conventional magnetic suspension bearing has some drawback. First, for avoiding the magnetic portion and stator generates magnetic linkage, the contacting area of upper-inner permeance ring and lower-inner permeance ring must be restricted. Thus the restriction of operating environment is very critical. Second, A ball bearing and a self-lubricated sleeve are located between two ends of the spindle, which further complicates the structure. U.S. Pat. No. 5,783,886 discloses a technique in which a spindle motor has a magnetic bearing. It has magnetic elements installed respectively on the spindle and the stator. The repulsive magnetic force enables the spindle to generate radial magnetic suspension against the stator to thereby avoid generating friction contact and wear. While it is easy to assemble and the axial magnetization is easy for mass production, the assembly positions of the spindle and the stator must be controlled accurately. A slight vibration from an external force will create obliquity. In other words, it adopts a magnetic suspension bearing design concept that is operable only in very precise conditions. U.S. Pat. No. 4,340,260 discloses another technique that has oblique magnetic elements installed on the stator and the spindle. It uses the property of repulsive magnetic force of the same magnetic polarity to enable the spindle and the rotator to generate suspension. It has a greater resistance against external impact and can prevent skewing, and magnetization is easier. U.S. Pat. No. 6,664,687 discloses a technique that applying a magnetic flux to the shaft. It has a shaft with a diminishing conical taper, and a sleeve arranged opposite the shaft has a conical concavity. The clearance between the shaft and the sleeve is filled with magnetic oil. The shaft 11 has the permanent magnet inside, and the sleeve is made of a magnetic material. When the shaft is tiled, the shaft with conical taper and the magnetic attraction between the shaft and the sleeve can help maintain the stable attitude of rotary section. However, above techniques are difficult to assemble, and the cost is higher.
In short, there are still many problems in the conventional techniques that need to be overcome.
Moreover, U.S. Pat. No. 5,506,459 discloses a technique in which a magnetically spining apparatus is balanced by circumscribing magnets is disclosed. It has a shaft with magnets, and a frame with support magnets. Particularly, the magnetic polarity dividing line of the magnets of the shaft are slightly higher than the magnetic polarity dividing line of the support magnets of the shaft for levitating the shaft to minimize friction at the pivot point. However, decreasing the friction of the shaft results the rotational devies (i.e. electric fan, hard disk, compact disk player, and so on.) rotate unstable.